Resistance material and method of manufacturing same



UNITED STATES PATENT- OFFICE.

JOSEPH P. MAXFIELD, OF MILTJBURN, AND

JERSEY, ASSIGNOBS TO WESTERN ELECTRIC COMPANY, INCORPO YORK, N. Y., A CORPORATION OF NEW YORK.

GEORGE 0. SMITH, OF EAST ORANGE, NEW

RESISTANCE MATERTAL AND METHOD OT MANUFACTURING SAME.

No Drawing.

To all whom it may concern:

Be it known that we, Josnrrr P. MAXFIELD and GEORGE 0. SMITH, citizens of the United States, residing at Mlllburn, in the county of Essex,State of New Jersey, and at East Oran e, in the county of Essex, State of New ersey, respectively, have invented certain new and useful Improvements in Returing Same, of which the followin is a full, clear, concise, and exact descriptlon. v This invention relates to resistance materials and more particularly to a granular type of resistance material suitable for telephone transmitters and a process of manufacturing such a material. i

To meet satisfactorily of a resistance material for use in telephone transmitters and similar places, it is of a decided advantage to have thegranules li ht and of substantially globular shape so t at they will not pack together and cause unsatisfactory operation of the transmitter itself. In certain types of transmitters, it is also of importance that the carbon particles be made light in order that their inertia may retard the movement of the diaphragm as little as ossible.

It is, therefore, t e object of the present invention to provide a granular resistance material, particularly for use in telephone transmitters, which'is substantially globular in shape, light in weight and has a firm hard surface.

To attain this result and in accordance with a feature of this invention, a resistance material is made bymixing ground carbon particles with a binder in such a way as to give a globular shape, and roasting the IHlX- ture to give the. desired resistance and surface firmness.

The preferable method of manufacturmg this type of resistance material is as follows:

A powdered carbon is obtained by reducing cane sugar to carbon in an open kettle bymeans of a lowflame and then grinding in a ball-mill until the resulting product.

is fine enough to pass sieve.

I The binder with which this powder is to be mixed is made by filling a pot approximately one-fourth full with cane sugar and then heating overa low flame,'the reduction through a 200 mesh Specification of Letters Patent.

1 being carried to 1ng approximately 'sistance Materials and Methods of Manufac-. Th'

the requirements in a rotating or .then inserted under .force itself into the small cavities and pores Patented Jan. 1'7, 1922.

Application filed m 12, 1919. Serial No. swam.

a point where the sugar gives 01f pungent odors and ceases to rise in the pot. Hot water is then poured in slowly until the mixture has a specific gravity of from 1.27 to 1.33. 1

i he powdered carbon and the caramel are mlxed together to produce a thick paste havthe consistency of putty. 1s mixture is then forced through a sieve, the mesh of which is approximately 15% greater than'the desired size of the resulting product, For the standard grades of carbon the size of this sieve will range from ten toforty mesh. This increased size of the material as sieved is necessary to provide for the shrinkage of material during the roasting operation.

The mixture, after being sieved, is placed ball-mill (but Without the balls) and is rotated for a twelve hours to three days, after which it is sieved to remove the smaller globules. The product is then dried in an oven at a temperature slightly below the .boiling point of water for a period of approximately 'four hours to remove all water from the binder graduall so as not to form cracks in the carbon g obules. It

customary steel period of from ATED, or NEW is then placed in crucibles where it is protected from oxidation by means of a covering of carbon which keeps out the air, and the temperature raised slowly so that at the end ofa period of two hours a temperature of approximately 300 C. is reached. The temperature is then raised to a temperature of 500 C. during the next hour and then raised rapidly to the final heat desired which is a bright red heat.

The product is allowed to cool and is then placed in a wire cage inside of a tank and all air exhausted. Additional caramel is pressure and tends'to in the surface of the lobules. The container with the carbon g with caramel is then placed in a centrifuge to remove all excess caramel and to keep the particles from sticking together. The carbon globules are then placed on drying trays which are maintained at a temperature slightly below boiling for a period of four hours, the grains being stirred at intervals of approximately one-half hour. The product is then heated in crucibles or an obules impregnated preferable to perform this operation as many as ten times. After the final impregnating operation, the product is. heated 1n crucibles to a final temperature ranging the product. By

from 1000? to 1400. C. depending upon the desired resistance of the carbon.

The resistance material made by following the above process not only has the advantage of freedom from packing as a re-.

sult of its substantially spherical shape and its lightness, but it also impedes the motion of light vlbrating systems a 'minimum amount. For detectophones and similar apparatus which must remain sensitive to very weak sounds, it is of importance that this impedance to motion be kept as low as possible. -The apparent density of the resistance material made by following in detail the process described is approximately .5 grams per cubic centimeter and slight variations from the specific process described may be made and the apparent density of the product kept within the limits of .4 to .7 grams per cubic centimeter. This light weight, however, does not involve a sacrifice of the wearing quality and permanence of ture of carbonization of the filler, it is posporous at the center but of increasing density toward the outer surface which is comparatively hard and smooth or to produce firm globules of uniform texture throughout.

What is claimed is:

1. A granular resistance material consisting of carbon granules substantially globularin shape and having an apparent density of approximately .50 grams per cubic centimeter.

2. A granular resistance material consist- .ing of carbon granules substantially globular in shape, said globules being of increasing density from the center toward the surface.

3. The method of manufacturing a resistance materlal which consists in forming then carbonized is following the process described and by small changes in the temperathen forcing similar material in a plastic state into the surface pores.

4. The method of manufacturing a resistance material which consists in mixing a resistance material with a binder, sieving the mixture, rotating the product to form particles substantially globular in shape, and roasting such globular material to give the desired resistance.

5. The method of manufacturing a resistance material which consists in grinding carbon to a powder of the desired fineness, mixing this powder with a binder to produce a material having ap roximately the consistency of putty, orcing this mixture through a sieve, rotating the sieved mixture to form globules substantially spherical in shape, roastin the globules, impregnating the globules with a filler, and again roasting the product to produce further carbonization to give the desired resistance.

,6. The method of manufacturing a resistance material which consists in grinding carbon to a powder of the desired fineness, mixing this powder with a caramel binder to produce a material having approximately the consistency of putty, forcing this mixture through a sieve, rotating the sieved filler, and again roasting the product to roduce further carbonization to give the esired resistance.

7 The method of manufacturing a resistance material which consists in grinding carbon to a powder of the desired fineness, mixing this powder with a caramel binder to produce a material having approximately the consistency of putty, forcing this mixture through a sieve, rotating the sieved mixture to form globules substantially s herical in shape, drying the globules s owly to remove all water, roastingthe globules, placing the roasted globules in a tank, exhausting all air from the tank, forcing caramel into the tank under pressure, removing all excess caramel by means of a centrifuge, and again roasting the product to produce further carbonization to give the desired resistance.

In witness whereof, we hereunto subscribe our names this 10th da of Jul A. D. 1919.

JOSEP PQM XFIELD. GEORGE 0. SMITH. 

